Integumentary System - Gland Development

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Introduction

The secretory glands associated with the integumentary system have similar embryonic origins and mechanisms of development, though are specialised by their locations and secretions. A key process and feature of all gland development is an epithelial-mesenchymal interaction(s). Gland secretion can also be regulated by a number of different mechanisms, including endocrine changes postnatally at puberty and during pregnancy.

The mammary gland development is covered in detail on a separate notes page.

Merocrine secretion animation.gif Apocrine secretion animation.gif Holocrine secretion animation.gif
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Some Recent Findings

  • Involvement of Wnt, Eda and Shh at defined stages of sweat gland development[1] "Sweat gland induction failed completely when canonical Wnt signaling was blocked in skin epithelium, and was accompanied by sharp downregulation of downstream Wnt, Eda and Shh pathway genes. The Wnt antagonist Dkk4 appeared to inhibit this induction: Dkk4 was sharply downregulated in β-catenin-ablated mice, indicating that it is induced by Wnt/β-catenin; however, its overexpression repressed Wnt target genes and significantly reduced gland numbers. Eda signaling succeeded Wnt. Wnt signaling was still active and nascent sweat gland pre-germs were still seen in Eda-null mice, but the pre-germs failed to develop further and the downstream Shh pathway was not activated. When Wnt and Eda were intact but Shh was ablated, germ induction and subsequent duct formation occurred normally, but the final stage of secretory coil formation failed. Thus, sweat gland development shows a relay of regulatory steps initiated by Wnt/β-catenin - itself modulated by Dkk4 - with subsequent participation of Eda and Shh pathways."
  • Hormones and the pilosebaceous unit [2] "The skin, especially the pilosebaceous unit, can be regarded as an endocrine organ meanwhile a target of hormones, because it synthesizes miscellaneous hormones and expresses diverse hormone receptors."
More recent papers  
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Search term: Gland Embryology

<pubmed limit=5>Gland Embryology</pubmed>

<pubmed limit=5>Gland Development</pubmed>

Textbooks

  • Human Embryology (2nd ed.) Larson Chapter 14 p443-455
  • The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Chapter 20: P513-529
  • Before We Are Born (5th ed.) Moore and Persaud Chapter 21: P481-496
  • Essentials of Human Embryology Larson Chapter 14: P303-315
  • Human Embryology, Fitzgerald and Fitzgerald
  • Color Atlas of Clinical Embryology Moore Persaud and Shiota Chapter 15: p231-236

Development of Glands

Two main surface types, sweat and sebaceous, with a number of specialized glands in integumentary regions (lacrimal, Meibomian).

  • both ectodermal in origin
  • form as ingrowth of ectoderm into the mesoderm

Secretion Mechanisms

Merocrine Apocrine Holocrine
Merocrine secretion animation.gif Apocrine secretion animation.gif Holocrine secretion animation.gif

Sweat Gland

Humans have two types of sweat glands are present in humans, differing in secretory mechanism, number, histological appearance and sweat composition.

  1. merocrine (~eccrine) sweat glands (majority)
  2. apocrine sweat glands (minority)
  • apocrine in axilla, pubic and nipple regions
    • see also mammary gland development

Sebaceous Gland

Adult skin sebaceous gland histology Adult skin sebaceous gland histology


Adult skin sebaceous gland histology

  • associated with hair development
  • except plans penis and labia minora
  • these glands secrete vernix

Vernix Caseosa

Newborn - vernix caseosa

(vernix, Latin, vernix = varnish, caseous = cheese=like) This is a specialized coating that forms in late development over the entire fetal surface. The main component, secreted sebum, is secreted by sebaceous glands. The other constituents are cells sloughed off the fetus's skin, and shed lanugo hair. The coating also has a high water content (80%) largely compartmentalized within fetal corneocytes (cells forming the stratum corneum). [3]

This coating develops intially in a cranio-caudal direction and can be absent in preterm infants.

Some functions include:

  • protection of the fetal skin from extraembryonic fluids amnion, urine
  • providing a slippery surface helps with parturition (birth)
  • acting as a biofilm barrier against infection

Lacrimal Glands

Lacrimal glands produce the aqueous tears that mix with Meibomian glands secretions to form a tear film coating the outer surface of the eye.

Human Development (based upon data from[4])

  • Carnegie stage 16-18 - formation of the lacrimal lamina
  • Carnegie stage 19-23 - formation of the lacrimal cord
  • Week 9+ - maturation of the excretory lacrimal system

Meibomian Glands

The Meibomian glands (glandulae tarsales) are sebaceous glands located at the margins of the upper and lower eyelids of humans and mammals.[5] The gland cells (meibocytes) secrete by a holocrine mechanism and produce constantly a lipid-rich secretion (meibum) that mix with with aqueous tears produced by lacrimal glands. These glands are also regulated through sex hormones, androgens have a supporting function while estrogens act antagonistically.

The glands were first described in 1666 by Heinrich Meibom (1638 - 1700) a German physician and anatomist.

Abnormalities

Alacrima

Term describes a range of abnormalities associated with lacrimal gland development. The most common genetic cause of alacrima is the Riley-Day syndrome.

Nasolacrimal Duct Obstruction

Drainage duct obstruction can be a common anomaly in children and can be caused by inflammation or fibrosis without any precipitating cause (primary classification) or by an acquired lacrimal drainage obstruction (secondary classification).

Vernix Caseosa Peritonitis

Not an abnormality of development, but a clinical term for a rare post-caesarean section complication due to spilt vernix caseosa at the time of caesarean section mediating a maternal inflammatory reaction.[6]

References

  1. <pubmed>25249463</pubmed>
  2. <pubmed>20224689</pubmed>
  3. <pubmed>11069626</pubmed>
  4. <pubmed>16879594</pubmed>| PMC2100314
  5. <pubmed>19660571</pubmed>
  6. <pubmed>19208257</pubmed>


Journals

Reviews

<pubmed>19681790</pubmed> <pubmed>8919141</pubmed> <pubmed>8196943</pubmed> <pubmed>19020961</pubmed>

Articles

<pubmed>19881987</pubmed> <pubmed>16179970</pubmed>

Search PubMed

Search Pubmed: Epithelial Gland Development | Sweat Gland Development | Sebaceous Gland Development | Eccrine Gland Development | Apocrine Gland Development | Lacrimal Gland Development | Meibomian Gland Development

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Cite this page: Hill, M.A. (2019, October 21) Embryology Integumentary System - Gland Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Integumentary_System_-_Gland_Development

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G